Wednesday, November 19, 2008

i thought that the subject sociology is damn borriingg.. but guess wut? as i flipped through the pages of the shouldnt-read-this-book (as mentioned by Aini) called educational sociology,my mind is twisting somewhere.

Previously, due to the unforgettable days of my practical with my students, i always bare in mind that- 'God, i'm not born to be a teacher'. The unbelievable behaviour of todays' teenagers were totally driving me out of this profession. Why bother to teach high schoolers? I got good results and should be better off continuing my studies to the higher level.

But the thought of becoming a teacher suddenly crossed my mind. But what made me? That is the power of the shouldnt-read-this-book. Basically, there's nothing much about the book. But as I studied the book (for the sake of the exam ;p), i realized that there's soo much space that I can use to improve myself in teaching. And maybe, the way I taught before, is the totally wrong way, which had covered my eyes from looking at the beautiful part of teaching!

A teacher is forever remembered as a teacher. You gained knowledge and skills from them. A teacher also teaches you how to behave and to survive in a community (The words came from the book ;p). But yes, I felt that to shape the behaviour and to instill the good values in our kids is my responsibility. If they succeed in life, being a respected person.. man!I'm their teacher!And if they turned out bad..man!I must have done something wrong.

To have myself sitting down and read the book, I couldnt help myself to realize that what a noble job that I am going to do. And now, I am fully ready with my whole heart, to dedicate myself to teach our kids!!Ya Allah, help me to keep these words in my mind..all the time..

Copper-based catalyst is used in water gas shift reaction to increase carbonyl, CO conversion. CO conversion produces hydrogen for industrial purposes. During the CO conversion, the copper-based catalyst deactivated due to the formation of copper crystallite. The surface area of copper-based catalyst is related to the rate of reaction of water gas shift reaction. This paper will report on the influence of surface area on the rate of reaction. It will also discuss the effect of promoter on the catalytic activity. The rate of reaction is measured in terms of rate per area of copper and rate per mass of catalyst.

1.0 Introduction

The water gas shift (WGS) reaction (CO + H2OCO2 + H2) plays an important role in carbonyl conversion and manufacturing hydrogen. Hydrogen is largely used in the production of hydrogen fuel cells. As stated by Pradhan et al [3], the success of hydrogen economy lies on the production of polymer electrolyte membrane (PEM) fuel cells where hydrogen is used primarily.

Water gas shift reaction is where carbon monoxide, CO is reacted with water to produce carbon dioxide and hydrogen gas. The significance of this reaction is to reduce the composition of CO in air by converting it to CO2. At the same time it produces hydrogen gas in a large scale for industrial purposes. This reaction which is highly exothermic, is a part of steam reforming of hydrocarbons.The reformated gas that comes out of a steam or autothermal reformer mostly contains a very high content of carbon monoxide [3].

Copper-based catalyst has been used in commercial WGS reaction to increase the conversion rate of CO to CO2 and H2. However, Mellor et al [2] mentioned that doubts arise in aspects of the nature of the active sites and also the role of additional components such as zinc oxide, alumina, and/ or ceria in WGS reaction. Cai et al [5] also discussed about the controversy of the oxidation state of copper, the role of zinc oxide, the active site for the reaction and the role of support, alumina.

Therefore, our current investigation is to develop an understanding of the copper based catalyst carried out under low temperature shift, LTS with the influence of the surface area on the reaction rate.

2.0 Experimental Procedure

2.1 Catalyst preparation

2.1.1 Alloy Preparation

According to Mellor et al [1], the Cu-Al and Cu-Ce binary alloys were prepared by firstly melting the required amount of copper and then adding required amount of aluminium. The alloy melt was stirred thoroughly and rapidly quench by pouring into agitated cold water. In some cases, a similar procedure was adopted to prepare the Cu-Zn-Al and Cu-Ce-Al ternary alloys. Both Cu-Al and Cu-Ce melt were made as described above, and cooled to below 420°C (melting point of Zn) and below -795°C (melting point of Ce). This procedure helps to avoid rapid vaporization of the lower melting Zn and Ce metal. Rapid stirring and cold water quenching of the melt completed the process.

2.1.2 Caustic leaching

Raney copper catalysts were prepared from alloys by a procedure similar to that adopted by Friedrich et al in Mellor et al [1]. During these experiments (preparation of CuO-Al2O3, CuO-CeO-Al2O3, CuO-CeO2 and Cuo-ZnO-Al2O3 catalyst), 20 g of alloy particles 0.50-1.180 mm in diameter were placed in 111 g of de-ionized water at 50

3.5°C. A solution containing 111 mL of 14.1M aqueous sodium hydroxide solution was added dropwise over 1 h to achieve a final leach concentration of 7.06 M. The extraction times used in the preparation of catalyst from ternary alloys of Cu-Zn-Al and Cu-Ce-Al were 1.0; 1.5; 2.0; 3.0 and 19.5 h. Binary alloy of Cu-Al and Cu-Ce were extracted for 1.5 h. The catalyst particles were then thoroughly washed with de-ionized water or distilled water until the pH of the wash water was 7. Then the copper-based catalysts were dried in air at 120°C for 12 h, crushed and calcined in air in a muffle furnace at 500°C for 5 h. Prior to testing, copper-based catalysts prepared were re-sieved in order to remove small copper fines generated during the leach reaction.

3.0 Results & Discussion

Table 1: Summary for the kinetics for water-gas shift reaction on Copper catalyst

Catalyst

Rate per area of Cu* /

10-6 mol m-2 s-1

Rate per mass of catalyst* / 10-6 mol g-1 s-1

Reaction Order

COa

H2Ob

CO2c

H2d

8% CuO-Al2O3

0.80

2.4

0.9

0.8

-0.7

-0.8

8% CuO-15%CeO2-Al2O3

0.83

0.75

0.7

0.6

-0.6

-0.6

8% CuO-CeO2

-

- 0.11

0.9

0.4

-0.6

-0.6

40% CuO-ZnO-Al2O3

0.79

7.6

0.8

0.8

-0.9

-0.9

*Rates of reaction for the WGS reaction on Cu based catalysts at 200ºC, 1 atm total pressure,

According to Pradhan et al [3], LTS reaction will result in higher CO conversion.This is due to the fact that WGS is an exothermic reaction. High temperature reactor converts bulk carbon monoxide from 2-3 vol % whereas low temperature unit further reduces CO level to less than 0.3 vol %.

High conversion rate of CO requires high surface area of copper-based catalyst. However, copper-based catalyst on its own will deactivate due to copper crystallite sintering. Therefore, there is a need to prepare Cu-based catalysts supported on various metal based oxides to resist copper crystallization. The crystallized copper is related to the surface area of the copper-based catalyst. When the size of the copper crystallite decreases, the surface area increases, resulting in higher rate of CO conversion.

A research conducted by Mellor et al [1] discovered that an increase in ZnO loading improved the contact between the copper surface and ZnO crystallites, thus, significantly improving the stability of copper-based catalyst. It was reported that ZnO played a role in assisting the copper crystals stabilizing process by acting as a suitable spacer material.

The role of aluminium is to produce high surface area of copper-based catalyst. However, according to Mellor [1] residual alumina in the active catalyst showed no beneficial effects. On the other hand, when copper is supported on CeO2,LTSCO oxidation is reported to be highly active (Tanaka et al (2003) in Pradhan et al [3]).

This experiment was carried out using copper-based catalyst promoted by different types of metal oxide to generate new active sites. According to an experiment carried out by Cai et al [5], it has been proven that the maximum use of active sites exhibit higher activity rate.

Based on Table 1, Koryabkina et al [6] explained that the power rate law expression serves as an indication for the common reaction mechanism whereby the temperature and concentration at the same conditions could be obtained for different samples.

Based on Table 1, the reaction rates per surface area of Cu are the same on all four samples. Looking at the rate of mass of catalyst, CuO-ZnO-Al2O3 showed the highest activity rate. Catalysts supported by Ce showed lower rates per unit of mass and lower copper surface area. However, Ce did not show any promotional effect in WGS reaction at the conditions tested, contrary to the effects shown on Pt or Pd. The constancy of rate per unit of copper surface area in table 1 indicates that the reaction occurs on copper only. Ce and ZnO do not affect the rates of reaction.

4.0 Conclusion

Based on the experimental data, it can be concluded that high surface area of copper-based catalyst will result in a higher rate of reaction. The surface area of copper is influenced by the type of metal oxide it is promoted with. According to the data used in this report, the copper-based catalyst promoted by CuO-ZnO-Al2O3 gave the highest reaction rate.

Sunday, August 17, 2008

this is a total disaster..i've been bending my head and knees, to quickly finish my work and make my way straight to kampung, but nothing seems to work yet.haaiihhh... there are only about 5 days left for my holiday to come to an end. Yet, this is not the reason for me to quickly pack up and leave this shabby-hostel-room. I'm trying to work on with my bundle of final year project works, and I slowly whispered to myself that this is going to end very soon..

Monday, June 16, 2008

This would be my first time writing something for the public views. Forgive me please, if my English is broken here and there. I'm only searching the opportunity to write since it has been sooo long since I wrote. I'm expecting myself to be a good story teller and would come up with something fresh to share with the world.Till here.. hehehe